Get the gauge to check the line spacing to ensure you get the correct size tool. You have the benefit, as you say, of wanting to renew what’s there (so much easier), but there’s nothing stopping you practicing and practicing on scrap wood from new. A couple of years ago I renewed the checkering on a Browning Citori for a friend - he had also bought a kit (though I had to get a new comb for the handle as his was too fine) and decided he didn’t want to. Honestly it’s not that bad. If you apply gentle pressure you don’t cut too deep. Best secure the wood in a suitable (well padded) table mounted vice, though experienced people just clamp it in their legs. If you’re new to it, as I was a few years back, just take your time - you don’t need to cut full depth on the first pass. I haven’t checked as of late, but there’s bound to be various tutorials on YouTube. Or practice on a friends gun first